DESCRIPTION

• Chronic diarrhea is defined as stool output >200 g/24 h in children and adults, or >10 g/kg/24 h in infants, that has occurred for >14 days.
• Should be differentiated from acute diarrhea, which is generally caused by enteric pathogens, is self-limiting, and has a duration of symptoms <14 days

EPIDEMIOLOGY

• Gender and genetic factors do not play a significant role in most cases of chronic diarrhea.
• Infectious chronic diarrhea is seen most commonly in low-resource settings.

PATHOPHYSIOLOGY

The two major categories of chronic diarrhea are osmotic and secretory. Inflammatory and motility disorders are important subcategories to consider.

• Osmotic diarrhea occurs when unabsorbable solute accumulates in the lumen of the small intestine and colon, increasing intraluminal osmotic pressure and resulting in excessive fluid and electrolyte losses in stool.
  • Osmotic diarrhea will improve with fasting.
  • Examples: lactase deficiency, glucose–galactose malabsorption, lactulose/polyethylene glycol use
• Secretory diarrhea occurs when the net secretion of fluid and electrolyte is in excess of absorption in the intestine:
  • Secretory diarrhea occurs independently of the osmotic load in the intestinal lumen.
  • Will not improve with fasting
  • The mechanisms for secretory diarrhea include the activation of intracellular mediators such as cAMP, cGMP, and calcium-dependent channels.
  • These mediators stimulate active chloride secretion from the crypt cells and inhibit the neutral coupled sodium chloride absorption.
  • Examples: congenital chloride diarrhea, vasoactive intestinal peptide (VIP), carcinoid
• Inflammation in the intestine can cause an alteration in mucosal integrity resulting in exudative loss of mucus, blood, and/or protein. Increased permeability and altered mucosal surface area may affect absorption and result in diarrhea due to malabsorption.
  • Examples: inflammatory bowel disease, bacterial enteritis
• Motility disorders affect intestinal transit time. Hypomotility can allow stasis from bacterial overgrowth and can lead to diarrhea.
  • Example: irritable bowel syndrome